Polyvinyl chloride, which is prepared by the polymerization of vinyl chloride, is one of the most useful of modern commercial plastics. Unfortunately, it is now believed that vinyl chloride in sufficient concentration is harmful. Accordingly, much research has been done recently on reducing the amount of vinyl chloride in polyvinyl chloride and in the environment in plants manufacturing polyvinyl chloride.
One of the preferred methods for the commercial preparation of polyvinyl chloride consists in carrying out the polymerization of vinyl chloride in an aqueous suspension. The slurry obtained from the polymerization reactor generally has a polyvinyl chloride content in the range of 20 to 60% by weight. More usually, the polyvinyl chloride content is in the range of 30 to 50% by weight. The slurry also contains residual vinyl chloride, which is present in an amount of less than 0.1% to 5%. My invention is directed to a method of removing a substantial amount of vinyl chloride from polyvinyl chloride-water slurries.
It is known to use steam to remove unreacted vinyl chloride from a water-polyvinyl chloride slurry. While use of steam can produce a resin containing low residual unreacted vinyl chloride the method is accompanied by some disadvantages. In a method employing a distillation column, using the counter-current effect of steam against the slurry, it is difficult to obtain the required residence time of the slurry in the columns without obtaining excessive plugging of tray internals. In a method employing an agitated staged gas-liquid contactor the steam velocities required are high enough to produce excessive slurry carry-over and back-mixing.